Barrier mechanism of camera

ABSTRACT

A barrier mechanism of a camera includes a cylindrical lens cover which has an aperture at its front face and which is supported to move between a photographing position and an accommodating position to the rear of the photographing position. At least one barrier is provided on the front end of the lens cover to open and close the aperture. A barrier opening and closing mechanism which opens and closes the barrier in association with the rotation of a cam ring is further provided. The barrier opening and closing mechanism includes a spring for biasing the barrier towards an open position, and an opening and closing pin which can be moved radially with respect to the lens cover. The pin closes the barrier when moved in the radial direction, and a closing lever is located at a predetermined position outside the lens cover and is biased to rotate to continuously press the opening and closing pin to close the barrier. The cam ring is located to normally prevent contact between the closing lever and the opening and closing pin. The cam ring is provided with an opening which permits the closing lever to rotate toward the opening and closing pin when the lens cover is moved to the accommodating position.

This is a continuation of application Ser. No. 07/318,336, filed Mar. 3,1989, now U.S. Pat. No. 4,989,027.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a barrier mechanism which opens andcloses an aperture located in front of a photographing lens in a camera.

2. Description of the Related Art

In place of a conventional removable lens cap which protects aphotographing lens of a camera, a lens cap (barrier) which is providedin a camera body is used particularly in a lens shutter type of camera.There are various known barrier mechanisms, in which barriers arelocated in front of the photographing lens, independently of the same infunction. The barriers are biased into an open position or closedposition by springs or the like. A photographer operates the barrier toopen or close the same against the spring force. However, such a manualoperation is not desirable particularly in an automatic lens shuttertype of camera in which almost all of the operations are automated.

Under these circumstances, the assignee of the present application hasproposed a barrier mechanism of a camera in which a cylindrical lenscover having at its front end an aperture is linearly movably supportedbetween a photographing position and an accommodating position locatedin rear of the photographing position. This is disclosed in JapaneseUnexamined Utility Model Publication Nos. 62-193228 and 62-193229 (U.S.Ser. No. 144,030). The lens cover is provided, on its outer periphery,with a cam ring which moves the lens cover between the photographingposition and the accommodating position in accordance with the rotationthereof. The lens cover has at its front end a pair of barriers foropening and closing the aperture and a barrier opening and closingmechanism which opens and closes the barriers in association with therotation of the cam ring.

In these above-mentioned barrier mechanisms an opening and closing pinwhich is biased into a barrier opening position is displaced by aprojection provided on the cam ring toward a barrier closing position.It has been found that the opening and closing pin can not be displacedby a predetermined stroke sufficient to close the barriers due to amanufacturing error or an assembly error, of the elements, thusresulting in a failure of a complete closure of the barriers.

Furthermore, in these barrier mechanisms, since the barriers, which arebiased to be opened by spring means, are closed against the springmeans, the largest reaction of the spring means is produced at theclosed position of the barriers. Accordingly, when the cam ring is inits lens accommodating position, it is necessary to apply a largeoperational force to the barrier opening and closing member in order tobias the barriers into the closed position. If the operational force isdecreased for some reason, the barriers can not be completely closed. Inparticular, the barriers are biased in a closed position by a springmeans. However, when the barriers are closed the reaction of the springmeans which tends to open the barriers is largest whereas the springforce which biases the closed position is at its smallest value. Thus,it is difficult to set a proper spring balance, and an impractical largespring may be needed.

In addition, there is a possibility that when the barriers are closed,they are not equally displaced, so that one of the barriers ismaintained to be slightly opened. This is because, according to theinventors' analysis, the force necessary to close the barriers is notequal for each of the barriers, whereas the opening and closing membertends to move to equally close each of the barriers. Therefore, one ofthe barriers (heavier barrier) reaches and passes a correct closedposition prior to the remaining barrier (lighter barrier), thusresulting in an excess displacement of the heavier barrier. Even if thelighter barrier comes into contact with the heavier barrier, it isimpossible to bring the heavier barrier back to the correct closedposition, resulting in an incomplete closure of the barriers.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a barriermechanism which is free from the drawbacks mentioned above and which cancertainly close the barriers even if there is a manufacturing orassembly error of the elements.

Another object of the present invention is to provide a barriermechanism in which a pair of barriers continuously biased to be openedare closed against a biasing force in a lens accommodating position. Anoperational force to be applied to the barrier opening and closingmember to close the barriers is substantially constant, or even if theoperational force is increased in accordance with the reaction of thespring, the increase is small.

Still another object of the present invention is to provide a barriermechanism in which a pair of barriers can be closed at a correct closedposition.

As mentioned before, the inventors have conceived that an incompleteclosure of the barriers occurs because of insufficient displacement(stroke) of the opening and closing pin which is continuously biased toopen the barriers. Accordingly, the solution is directed to guaranteeinga sufficient displacement of the opening and closing pin in any state.

Namely, according to the present invention, there is provided a barriermechanism of a camera comprising a cylindrical lens cover which has atits front face an aperture and which is supported to move between aphotographing position and an accomodating position being theaccommodating position in rear of the photographing position. The lenscover is provided with a cam ring which moves the lens cover between thephotographing position and the accommodating position in accordance withthe rotation thereof. At least one barrier is further provided on thefront end of the lens cover to open and close the aperture, and abarrier opening and closing mechanism is provided which opens and closesthe barrier in association with the rotation of the cam ring. Thebarrier opening and closing mechanism comprises spring means for biasingthe barrier towards an open position, and an opening and closing pinwhich can be moved in the radial directions of the lens cover. Theopening and closing pin closes the barrier against the spring means whenthe opening and closing pin moves in one radial direction. A closinglever is located at a predetermined position outside the lens cover, andis biased to rotate to continuously press the opening and closing pintoward a particular radial direction (that is, toward its closingposition). The cam ring is provided in a location to normally preventcontact between the closing lever and the opening and closing pin, andthe cam ring is further provided with an opening which permits theclosing lever to rotate toward the opening and closing pin when the lenscover is moved to the accommodating position.

With this arrangement, when the opening of the cam ring is registeredwith the closing lever, that is, when the cylindrical lens cover ismoved backward to the accommodating position, the closing and openingpin can be fully pushed (displaced) by the rotational biasing force ofthe closing lever, so that no failure of complete closure of thebarriers occurs.

The present invention also proposes a barrier mechanism that compensatesfor an increase of spring reaction which is produced when the barriersare closed, by increasing arm length of the barrier closing member, sothat the barriers can be closed with a small force. Namely, if thereaction of the spring increases, the arm length of the lever forrotating the barriers against the spring force is correspondinglyincreased. With this arrangement, the operational force to be applied tothe lever can be maintained substantially constant or at least, theoperational force does not increase in propotion to the reaction of thespring.

Furthermore, the present invention proposes a mechanism in which, when apair of barriers are closed, a lighter barrier is first brought into theclosed position or into an excess closed position beyond the closedposition, and the heavier barrier is then moved to the closed position.With this arrangement, since the lighter barrier is brought back to thecorrect closed position by the heavier barrier, both the barriers can bealways closed at the correct closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIGS. 1 and 2 are sectional views, taken along the line I--I in FIG. 6,showing a barrier mechanism of a camera according to an embodiment ofthe present invention, depicting open and closed positions of thebarriers, respectively;

FIGS. 3 and 4 are sectional views similar to FIGS. 1 and 2, according toanother embodiment of the present invention, respectively;

FIG. 5 is a skeleton diagram showing a relationship between an openingand closing pin and intermediate levers in an embodiment illustrated inFIGS. 3 and 4;

FIG. 6 is a longitudinal sectional view of a lens shutter type of camerahaving a barrier mechanism according to the present invention;

FIGS. 7 and 8 are sectional views similar to FIGS. 1 and 2, according tostill another embodiment of the present invention, respectively;

FIGS. 9 and 10 are enlarged sectional view and perspective view of aninclinable plate in relation to an opening and closing pin shown inFIGS. 7 and 8; and,

FIGS. 11 and 12 are sectional views similar to FIG. 9, according to twodifferent embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The illustrated embodiments are directed to a lens shutter camera havinga zoom lens.

FIG. 6 shows a whole construction of a zoom lens shutter camera having abarrier mechanism 30 according to the present invention. A camera body11 has a stationary barrel 13 which is secured to the front face thereofby set screws 12. On the rear face of the body 11 are provided an innerrail 11a and an outer rail 11b which comes into contact with a pressureplate 15 provided on a back cover 14, so that a film moves in a spacedefined between the pressure plate 15 and the inner rail 11a. A finderoptical system 16 is provided above the body 11. The body 11, the finderoptical system 16 and the stationary barrel 13 are covered by a camerabody case 17.

A cam ring 20 is fitted onto the inner periphery of the stationarybarrel 13 so as to rotate and move in the optical axis directions. Thecam ring 20 has cam grooves 20a and 20b for moving front and rear lensgroups L1 and L2 in the optical axis directions along predeterminedtracks defined by the profiles of the cam grooves. A pin 23a provided ona cam follower ring 23 for the front lens group is fitted in the camgroove 20a. The pin 23a is also fitted in a linear movement guide groove13a which is formed in the stationary barrel 13 to extend in the opticalaxis direction, so that the cam follower ring 23 can move only in theoptical axis directions but can not rotate.

The cam follower ring 23 for the front lens group is provided with aguide pin 23b which extends in parallel with the optical axis toslidably support a cam follower ring 24 which supports the rear lensgroup L2. A pin 24a provided on the cam follower ring 24 is fitted inthe cam groove 20b of the cam ring 20 through a groove 23c formed in thecam follower ring 23.

The cam follower ring 23 for the front lens group has a lens shutterunit 25 secured to the front portion thereof. The lens shutter unit 25is screw-engaged by a lens ring 26 which supports the front lens groupL1 through helicoids 25b and 26c. The lens shutter unit 25 rotates thedrive pin 25a provided thereon by an angular displacement correspondingto a distance signal from an object distance measuring device (notshown) and opens and closes a shutter sector 25b in accordance with ameasuring light signal from a photometer (not shown). The drive pin 25ais engaged by an association arm 26a secured to the front lens ring 26,so that the front lens ring 26 moves in the optical axis directions inaccordance with the angular displacement of the drive pin 25a to adjustthe focus.

The cam ring 20 is driven to rotate by a drive motor (not shown) througha gear train. When the cam ring 20 rotates, the front cam follower ring23, and accordingly, the front lens group L1 move in the optical axisdirections in accordance with the profiles of the cam groove 20a and thelinear movement guide groove 13a. In addition, the rear cam followerring 24, and accordingly, the rear lens group L2 move in the opticalaxis directions in accordance with the profile of the cam groove 20b tochange the spatial distance between the front and rear lens groups L1and L2, thus effecting zooming. When the cam ring 20 rotates to one ofthe extremities of the angular displacement, the lens groups L1 and L2are moved to the accommodating position which is retracted from thephotographing position.

A back adjustment mechanism is provided between the cam ring 20 and thestationary barrel 13. The cam ring 20 is provided on its outer peripherywith a circumferential groove 27 in which a thrust member 28 supportedon the stationary barrel 13 for the axial movement is fitted. Thus, theback adjustment in which the position of the cam ring 20, andaccordingly, the positions of the front and rear lens groups L1 and L2are adjusted to make the focal plane coincidental with the film planecan be effected by the adjustment of the axial position of the thrustmember 28. After the back adjustment is effected, the thrust member 28is secured to the stationary barrel 13 by the set screws 29.

A cylindrical lens cover is secured to the cam follower ring 23. Thecylindrical lens cover 31 has at its front face an aperture frame 32having an aperture 32a secured thereto. A barrier ring plate 33 issecured to the inner periphery of the lens cover 31. The barriermechanism 30, which constitutes one of the most significant features ofthe present invention, is supported by the front and rear faces of thebarrier ring plate 33.

FIGS. 1 and 2 show an embodiment of the barrier mechanism 30. FIGS. 1and 2 are sectional views taken along the line I--I in FIG. 6, viewedfrom rear. The barrier ring plate 33 has a pair of barriers 34 which arepivoted to the front face of the barrier ring by pins 35 to open andclose the aperture 32a. The barriers 34 are opposed to each other in asymmetrical arrangement and have barrier plate portions 34a whichproject into the aperture 32a and are driven by arm portins 34b whichextend substantially perpendicularly to the associated barrier plateportions 34b with respect to the pins 35.

The driven arm portions 34b have operation pins 36 which extend throughholes 33a to project to the back face of the barrier ring plate 33. Theoperation pins 36 are engaged at their outside outer peripheries by apair of elastic leg portions 37a of a single wire spring 37 to bias thebarriers 34 in a direction in which the barrier plate portions 34a openthe aperture 32a. Accordingly, when no external force is applied to thebarriers 34, the latter always open the aperture 32a.

The wire spring 37, which is made of metal, has a U-shaped centralportion 37b which engages with a support pin 38 provided on the barrierring plate 33. A change in spring force due to a change of environment,such as temperature or humidity, does not occur, nor does deteriorationdue to aging occur. Thus, the wire spring 37 can continuously bias thebarriers 34 in an open position with a stable constant spring force.

The operation pins 36 of the driven arm portions 34b are engaged attheir inside outer peripheries by respective operational arms 39a of apair of right and left intermediate arms 39 which are pivoted to thebarrier ring 33 by respective pins 40. The intermediate arms 39 have apair of driven arms 39b which extend in opposite directions to therespective operational arms 39a with respect to the associated pins 40to come into engagement with opposite drive arms 41a of an opening andclosing pin 41. The opening and closing pin 41 is movably guided by aguide cylinder 42 which is to the barrier ring 33 in position extendingradially from the center of the barrier ring 33. The head of the openingand closing pin 41 faces an association rectangular hole 43 formed inthe lens cover 31. The opening and closing pin 41 is located in anoutermost position in which the pin 41 is outwardly and radiallyprojected by the spring force of the wire spring 37 when no externalforce is applied to the pin 41. The wire spring 37 and the intermediatearms 39 are provided on the back surface of the barrier ring 33.

The rotating cam ring 20 which surrounds the outer periphery of thecylindrical lens cover 31 is provided on its front end surface with anopening (recess) 45 which is registered with the rectangular hole 43when the lens cover 31 comes to the accommodationg position. Thestationary barrel 13 has a closing lever 47 pivoted thereto by a shaft46. The closing lever 47 is biased by a torsion spring 48 provided onthe shaft 46, so that the operational end 47a of the closing lever 47extends through the rectangular hole 43 into the inside of the lenscover 31 to push the opening and closing pin 41. Since the opening 45 isprovided in the cam ring 20 which rotates around the lens cover 31, theoperational end 47a of the closing lever 47 extends through the opening45 into the rectangular hole 43 only when the operational end 47a isregistered with the opening 45. Otherwise, the operational end 47a ofthe closing lever 47 is maintained so as not to enter the rectangularhole 43 by the outer surface of the cam ring 20. The operational end 47aof the closing lever 47 is registered with the opening 45 only when thecylindrical lens cover 31 rotates to the accommodating position.

In the barrier mechanism 30 as mentioned above, the operational end 47aof the closing lever 47 extends through the opening 45 and therectangular hole 43 which is registered therewith to press the openingand closing pin 41 with the help of the spring force of the torsionspring 48. This occurs when the lens groups L1 and L2 are located in theaccommodating position through the cam grooves 20a and 20b of the camring 20. As a result, the right and left drive arms 41a of the openingand closing pin 41 push the driven arms 39b of the intermediate arms 39to rotate the same against the spring force of the wire spring 37.Consequently, the barriers 34 rotate about the associated pins 35 toclose the barrier plate portions 34a (FIG. 2). The force for closing thebarriers is obtained by the spring force of the torsion spring 48 whichis set to fully overcome the spring force of the wire spring 37.Accordingly, it is possible to cause a displacement (stroke) of theopening and closing pin 41 sufficient to close the barrier plateportions 34a, thus resulting in no failure of closure of the barrierplate portions 34a.

On the other hand, when the cam ring 20 is rotated to a photographingposition in which a picture can be taken from the extremitycorresponding to the lens accommodating position, the end 45a of theopening 45 moves (raises) the closing lever 47 outwardly and radiallyagainst the torsion spring 48, so that the operational end 47a comesinto slide contact with the outer peripheral surface of the cam ring 20.In this state, since no barrier closing force is applied to the openingand closing pin 41, the barriers 34 are opened by the wire spring 37(FIG. 1).

After photographing is completed, the cam ring 20 is rotated to the lensaccommodating position, and the operational end 47a of the closing lever47 enters the opening 45 to occupy a position shown in FIG. 2. Namely,the barriers 34 are automatically closed again.

FIGS. 3 and 4 show another embodiment of the present invention. Thedifferences between the first embodiment illustrated in FIGS. 1 and 2and the second embodiment illustrated in FIGS. 3 and 4 reside in theshapes of the drive arms 41a of the opening and closing pin 41, and thedriven arms 39b of the intermediate arms 39 which bear against the drivearms 41a. Namely, in the second embodiment, the drive arms 41a extend inthe radial directions of the cam ring 20 and have sharp front ends. Onthe other hand, the driven arms 39b of the intermediate arms 39 areshaped so that when the barriers 34 are in an open position, the drivenarms 39b come into contact with the associated drive arms 41asubstantially at a right angle. FIG. 5 shows a skeleton diagram showinga relationship between the opening and closing pin 41 and theintermediate levers (arms) 39.

The operation for opening and closing the barriers 34 in the secondembodiment is substantially same as that of the first embodiment. Itshould be, however, appreciated that when the opening and closing pin 41is displaced by the closing lever 47, the contact point (a point atwhich the force acts) between the drive arms 41a and the associateddrive arms 39b moves outward away from the pins 40, so that the armlength of the driven arms 39b is substantially increased (FIG. 4).Therefore, if the opening and closing pin 41 is pressed and displacedwith the same force, the force which tends to close the barriers 34through the intermediate arms 39 increases as the opening and closingpin 41 moves inward. As a result, the increased force compensates forthe reaction of the wire spring 37 which increases as the barriers 34are closed. Therefore, with this arrangement, the operational force ofthe opening and closing pin 41 does not substantially change. This makesit possible to use a stronger wire spring 37 or a weaker torsion spring48.

This will be explained below in more detail with reference to FIG. 5.

Suppose that the opening and closing pin 41 which is pressed by theclosing lever 47 is moved from a position shown at a solid line to aposition shown at an imaginary line in the course of closure of thebarriers. The effective length of the driven arms 39b of theintermediate levers 39 is increased from a to a'. On the contrary, theeffective arm length of the operational arms 39a (the distance betweenthe pins 40 and the associated operational pins 36) is substantiallymaintained constant as b. Thus, the operational force F to be applied tothe opening and closing pin 41 can be maintained constant or anyincrease of the operational force F if necessary is remarkably reduced,in spite of the increased reaction of the wire spring 37. As the openingand closing pin 41 is pressed and displaced with the same force F, theforce which tends to open the barriers 34 through the intermediatelevers 39 increases as the opening and closing pin 41 moves inward tocorrespond to the reaction of the wire spring 37 which increases as theopening angular displacement of the barriers 34 increases. Thus, abarrier opening and closing mechanism in which no change or only slightchange of the operational force of the opening and closing pin 41 takesplace can be realized.

It can be easily understood that even if the arm length b of theintermediate levers 39 mentioned above increases as the barriers areclosed, the philosophy of the present invention can be applied so longas the arm length a has a larger change (i.e. a relationship in whichthe ratio a/b increases).

FIGS. 7 through 10 show still another embodiment of the presentinvention. In the third embodiment illustrated in FIGS. 7-10, theimprovement is addressed to the prevention of incomplete closure of thebarriers 34, wherein the barriers 34 are brought into contact with eachother at a correct closed position. The feature of the third embodimentis a provision of an inclinable plate 41A which constitutes drive arms41a' of the opening and closing pin 41 and which is made of a materialseparate from the opening and closing pin 41.

Namely, the drive arms 41a' which come into contact with a pair ofoperational arms 39a of the intermediate levers 39 are formed by amember separate from the opening and closing pin 41, as can be seen inFIGS. 9 and 10. The drive arms 41a' are provided on the opposite ends ofthe inclinable plate 41A through which the opening and closing pin 41extends with a play. The opening and closing pin 41 has fulcrumprojections 41b which are located at the center of the intermediatelevers 39, so that the inclinable plate 41A can be inclined about thefulcrum projections 41b, relative to the opening and closing pin 41. Theinclinable plate 41A is maintained at its initial position in which itlies perpendicularly to the axis of the opening and closing pin 41, bythe pair of intermediate levers 39 located in a symmetrical arrangement,when no external force is applied to the inclinable plate 41A. Theopening and closing pin 41 is radially projected most by the springforce of the wire spring 37 through the inclinable plate 41A.

In the barrier mechanism 30 mentioned above, when the cam ring 20 isrotated to the photographing position in which a picture can be takenfrom one of the extremities of the angular displacement corresponding tothe lens accommodating position, the closing lever 47 is rotated in thecounterclockwise direction in FIGS. 7 and 8 against the torsion spring48 by the end 45a of the opening 45, so that the operational end 47a ofthe closing lever 47 comes into slide contact with the outer peripheralsurface of the cam ring 20. In this state, since no barrier closingforce is applied to the opening and closing pin 41, the barriers 34 areopened by the spring force of the wire spring 37. In this position, theinclinable plate 41A lies in a plane perpendicular to the opening andclosing pin 41 (FIG. 7).

After photographing ends, when the cam ring 20 is rotated to the lensaccommodating position, the operational end 47a of the closing lever 47enters the opening 45 of the cam ring 20 to project into the rectangularhole 43. As a result, the opening and closing pin 41 is pressed by thespring force of the torsion spring 48, so that the right and left drivearms 41a' of the inclinable plate 41A which is pressed through thefulcrum projections 41b press the driven arms 39b of the intermediatearms 39 to rotate the same against the spring force of the wire spring37. Consequently, the pair of barriers 34 are rotated about theassociated pins 35 to close the barrier plate portions 34a (FIG. 8).

If there is a difference in operational force of the drive arms 41aduring the closure of the barriers, the inclinable plate 41A inclines(rotates) about the fulcrum projections 41b of the opening and closingpin 41 (FIG. 9). Namely, the drive arm 41a' (the left drive arm in FIG.9) of the heavier barrier is pressed outward, so that the drive arm 41a'(the right drive arm in FIG. 9) of the lighter barrier is moved inward.In this state, if the opening and closing pin 41 is pushed inward, thelighter barrier 34 which is closed by the right intermediate lever 39 inFIG. 9 is first closed and is then stopped at an excess closed positionbeyond the correct closed position. A further displacement of theopening and closing pin 41 causes the inclinable plate 41A to move tocorrect the inclination relative to the opening and closing pin 41,thereby to press the intermediate lever 39 through the left drive arm41a ' in FIG. 9. As a result, the heavier barrier 34 is closed to comeinto contact with the lighter barrier 34 which has been excessivelyclosed. Note that the lighter barrier can be easily moved by the heavierbarrier, so that the pair of barriers 34 correctly close the aperture32a.

FIGS. 11 and 12 show two different embodiments of the present invention.In these modifications, no fulcrum projection 41b is provided on theopening and closing pin 41. In FIG. 11, the inclinable plate 41B has anarchwise cross sectional shape, so that the apex portion (raisedportion) thereof constitutes a fulcrum which comes into contact with theplane portion 41c of the opening and closing pin 41 to be inclined. InFIG. 12, the inclinable plate 41C is made of a flat plate which comesinto contact with the plane portion 41d of the opening and closing pin41.

According to the embodiment shown in FIG. 11, functional and technicaladvantages similar to those in FIGS. 7 and 8 can be obtained. Inparticular, the embodiment illustrated in FIG. 12 can be advantageouslyused when there is a large difference in load applied to the barriers.

Finally, it is possible to move the opening and closing pin 41 in thebarrier closing direction by means other than the closing lever 47biased by the spring. For instance, the opening and closing pin 41 canbe moved to close the barriers by a part of the cam ring 20 or a closingmember which is associated therewith.

We claim:
 1. A barrier mechanism of a camera, comprising a cylindrical lens cover having a front end with an aperture therein, said barrier mechanism being supported to move between an open, photographing position and a closed, accommodating position, said cylindrical lens cover being provided with a cam ring which moves said cylindrical lens cover between said photographing position and said accommodating position in accordance with a rotation of said cam ring, at least two barriers which are provided on said front end of said cylindrical lens cover to open and close said aperture in said cylindrical lens cover, and a barrier opening and closing mechanism which opens and closes said barriers in association with said rotation of said cam ring, wherein said barrier opening and closing mechanism comprises spring means for biasing said barriers to said open position; an opening and closing pin which can be moved in radial directions of said cylindrical lens cover and which closes said barriers against said spring biasing means when said opening and closing pin moves in one radial direction; and a closing lever which is located at a predetermined position outside said cylindrical lens cover and which is biased to rotate and press said opening and closing pin to close said barriers, said cam ring being located to prevent said closing lever from contacting said opening and closing pin when said barriers are to be in said photographing position, means for permitting said closing lever to engage said opening and closing pin to close said barriers, without any radial force being exerted on said opening and closing pin by said cam ring, when said cylindrical lens cover is moved to said accommodating position, said means for permitting said closing lever to engage said opening and closing pin being associated with said cam ring.
 2. The barrier mechanism of claim 1, further comprising a barrier ring plate having a front face, wherein said barriers are pivotable to said front face of said barrier ring plate.
 3. The barrier mechanism of claim 1, wherein said spring means comprises a wire spring.
 4. The barrier mechanism of claim 1, further comprising at least one intermediate lever which transmits the operation of said opening and closing pin to at least one of said barriers.
 5. The barrier mechanism of claim 4, further comprising a barrier ring plate having a rear face, wherein each said intermediate lever is pivotable to said rear face of said barrier ring plate. 